The term "air conditioning" has been broadly defined to mean the maintenance of certain aspects of the environment within a defined space. Environmental conditions, such as air temperature and motion, moisture level, and concentration of various pollutants, are generally encompassed by the term.
Comfort air conditioning refers to control of spaces inhabited by people to promote their comfort, health and productivity. Spaces in which air is conditioned for comfort include residences, offices, institutions, sports arenas, hotels, factory work areas, and so on.
With recent trends being directed to maintaining quality levels of clean air as today's society has become more health and environmentally aware, a greater emphasis is being placed on the purification components of air conditioning systems. At its simplest level, air pollution control suggests a background knowledge concerning desirable criteria for clean air, the ability to relate air quality to levels of emissions, the development of emission limits or other control standards, the means to measure such emissions and air quality, and the availability of practical techniques to reduce air pollutants. Therefore, although increasing attention as been directed to process alterations to reduce air-pollutants in general, great reliance is still placed upon physical removal processes.
A complete air conditioning system is capable of adding and removing heat and moisture. Moisture is typically added to provide an environment comfortable for human occupancy. In addition, such systems can filter dust and odorants from the space or spaces it serves. Winter air conditioning systems are designed to heat, humidify and filter for winter comfort while summer air conditioning systems cool, dehumidify and filter. Typically, design conditions are such that both winter and summer air conditioning can be maintained by multiple independent subsystems tied together by a single control.
To control humidity and air purity (and in most systems for controlling air temperature), a portion of the air in the space is withdrawn, processed, and returned to the space to mix with the remaining air. Such air-handling units generally contain a filter, a cooling coil, a heating coil, and a fan in a suitable casing.
Although the filter removes dust and other pollutants from both return and outside air, the gaseous pollutant removal efficiencies and performance of such filters are still considerably less than other low cost air purification alternatives (e.g., ventilation) because of the very low concentrations of pollutants found in areas of human occupancy. For example, low concentrations of pollutants such as formaldehyde, sulfur dioxide, and nitrogen dioxide are generally found in levels less than 100 ppb (parts per billion). As such, current filter systems are not cost effective for active indoor air quality control, i.e., human habitats, office buildings, etc. In these applications for example, the air pollution removal (APR) devices performance is limited, e.g., pollutant removal efficiency, E.sub.c &lt;50% and reagent utilization (the amount of reagent used of total reagent available), .mu..sub.R &lt;10%. Therefore, a need exists to improve the performance of such filters while maintaining acceptable capital and operating costs. Only then will APR devices become an integral part of air conditioning systems and an economically attractive alternative in environments harboring low levels of gaseous pollutants.